A conventional biosensor is provided with a development layer for developing an inspection target solution, a reagent immobilization part immobilized on a part of the development layer and a reagent holding part where a marker reagent which can be eluted by development of the inspection target solution is held, wherein a bonding amount of the marker reagent in the reagent immobilization part is measured, thereby qualitatively or quantitatively measuring components to be measured in the inspection target solution. An example of such a biosensor is an immuno-chromatographic sensor.
The immuno-chromatographic sensor is generally constituted by an application layer where an inspection target solution is applied, plural development layers, and a water absorbing layer at the end of the development layers. These development layers have an antibody immobilization part where an antibody for components to be measured in the inspection target solution is immobilized in a part thereof, and a marked antibody is held in a marker reagent holding part on the application layer side with respect to the antibody immobilization part, in a dry state where the marked antibody can be eluted by the inspection target solution.
In this immuno-chromatographic sensor, a required amount of inspection target solution is applied to the application layer and the inspection target solution permeates porous materials provided on the development layers, thereby starting the measurement.
As methods for applying the inspection target solution, there have been employed a method for soaking an application part in the inspection target solution for a definite period of time, a method for applying a predetermined amount of inspection target solution employing a high-precision dispenser, a dropper, or the like, a method for directly applying the inspection target solution to the application part for a definite period of time at urination when urine or the like is taken as the inspection target solution, or the like.
A measurement result of the immuno-chromatographic sensor is detected by a marked antibody bonded to the antibody immobilization part. With respect to this marked antibody, a typical marker is gold colloid particles, by which the bonding in the antibody immobilization part can be seen, and the measurement result can be obtained visually. While a sandwich reaction of an antigen antibody reaction by which a complex of an immobilized antibody, a measurement target, and the marked antibody is formed is taken as a measurement principle here, the measurement result can also be obtained by confirming a bonding state of the marker reagent in the antibody immobilization part or an antigen immobilization part even when other competitive reactions are similarly taken as measurement principles.
Further, while a visual qualitative judgement is required with respect to the measurement result by the above-mentioned sandwich reaction, in a case where a semi-quantitative or more accurate judgement is required for a required measurement result, there are also a method for reading by a transparent mode employing an optical reading device, which is disclosed in Japanese Published Patent Application No. Hei. 10-274624, and a method for taking-in a measurement result as an image by a camera or the like to be processed arithmetically, which is disclosed in Japanese Published Patent Application No. Hei. 10-274653.
In recent years, a quick, simple, and accurate measuring device which is easily available at a low cost has been desired with a concept of POC (Point of Care) in the medical and diagnostic scene. However, according to the above-described conventional methods, when the inspection target solution, which is blood for example, is applied to a sensor part, it has been required that blood is collected employing an injector, generally subjected to an operation for separating blood corpuscles as concrete components and blood plasma employing a centrifugal separator, and applied to the sensor part employing a tool such as a dispenser or a dropper.
This method for collecting blood by an injector requires special skills in medical technology, and the necessity of the centrifugation operation makes it impossible to perform self-measurements in a household or by individuals not having the ability to perform centrifugation process.
Further, since the tool such as a dispenser is required for quantitatively measuring the inspection target solution, the operation becomes complicated.
Further, when the inspection target solution is urine or the like, there is a method in which urine is collected in a container such as a paper cup once and a part of the sensor is soaked therein for a definite period of time, a method in which collected urine is applied employing a dispenser, dropper, or the like as in the case of blood, when a predetermined volume of inspection target solution is required to be quantitatively measured, and a method in which urine is directly applied to an application part for a definite period of time at urination in the case of a relatively low-accuracy sensor which does not require quantitative accuracy in a measurement. In these methods, however, urine is required to be collected in a paper cup or the like once, or there is no means for accurately defining the volume of the inspection target solution in a case where urine is directly applied, resulting in restriction to a qualitative measurement with low accuracy and the like.
The present invention is made to solve the above-mentioned problems and has for its object to provide a biosensor which requires no sophisticated device or operation and can perform a simple and high-accuracy measurement even with a small volume of inspection target solution.